Process for producing anhydrides of aromatic polycarboxylic acids

ABSTRACT

A process for producing anhydrides of benzenepolycarboxylic acids by the vapor-phase oxidation of aromatic hydrocarbons selected from the group consisting of naphthalene, octahydroanthracene and polyalkylbenzenes containing at least two alkyl substituents in ortho position to one another and having the general formula   WHEREIN R1 and R2 are alkyl radicals having a straight or branched chain and containing 1 to 6 carbon atoms and R3 and R4 are radicals selected from the group consisting of hydrogen and alkyl radicals containing 1 to 4 carbon atoms, the total number of carbon atoms of said polyalkylbenzenes being no higher than 18, said process comprising oxidizing said aromatic hydrocarbons at a temperature of between about 300* and 550*C and in the presence of a catalyst consisting of a refractory carrier and vanadium oxide, said catalyst prepared by impregnating said refractory carrier with an oxytrihalide of vanadium in which the halide is selected from the group consisting of chlorine and bromine, hydrolyzing said oxytrihalide and vanadium and then calcining said catalyst.

United States Patent [191 Draguez de Hault et a1.

[ PROCESS FOR PRODUCING ANHYDRIDES OF AROMATIC POLYCARBOXYLIC ACIDS [75] Inventors: Emmanuel R. E. G. Draguez de Hault, Waterloo; Henri R. Debus, Meise; Marcel Van Tongelen, Diegem, all of Belgium [73] Assignee: Labofina S.A., Brussels, Belgium [22] Filed: Oct. 26, 1973 [21] Appl, No.: 410,275

[30] Foreign Application Priority Data FOREIGN PATENTS OR APPLICATIONS 164,785 6/1921 United Kingdom OTHER PUBLICATIONS Takei, Chem. Abstracts, (1968), Vol. 69, 622l2d.

Primary ExaminerHenry R. Jiles Assistant ExaminerBemard I. Dentz Attorney, Agent, or Firm-Bacon & Thomas Dec. 9, 1975 57 ABSTRACT A process for producing anhydrides of benzenepolycarboxylic acids by the vapor-phase oxidation of aromatic hydrocarbons selected from the group consisting of naphthalene, octahydroanthracene and polyalkylbenzenes containing at least two alkyl substituents in ortho position to one another and having the general formula wherein R and R are alkyl radicals having a straight or branched chain and containing 1 to 6 carbon atoms and R and R are radicals selected from the group consisting of hydrogen and alkyl radicals containing 1 to 4 carbon atoms, the total number of carbon atoms of said polyalkylbenzenes being no higher than 18, said process comprising oxidizing said aromatic hydrocarbons at a temperature of between about 300 and 550C and in the presence of a catalyst consisting ofa refractory carrier and vanadium oxide, said catalyst prepared by impregnating said refractory carrier with an oxytrihalide of vanadium in which the halide is selected from the group consisting of chlorine and bromine, hydrolyzing said oxytrihalide and vanadium and then calcining said catalyst.

12 Claims, No Drawings 1 PROCESS FOR PRODUCING ANHYDRIDES OF AROMATIC POLYCARBOXYLIC ACIDS This invention relates to a process for producing anhydrides of aromatic polycarboxylic acids.

The anhydrides of aromatic polycarboxylic acids have a wide variety of applications, more particularly the manufacture of plasticizers, snythetic resins and fibers. The most often used anhydrides are the phthalic and pyromellitic anhydrides. These anhydrides may be prepared by vapor-phase oxidation of aromatic hydrocarbons selected from the group consisting of naphthalene, octahydroanthracene and aromatic hydrocarbons having at least two alkyl substituents in ortho position and having the general formula wherein R and R are alkyl radicals which may be straightor branched-chain and which contain from I to 6 carbon atoms and which may be the same or different, R and R are hydrogen or an alkyl radical of from I to 4 carbon atoms and which may be the same or different, the total number of carbon atoms of said alkylaromatic hydrocarbons being no greater than 18.

The vapor-phase oxidation of these alkylaromatic hydrocarbons generally is carried out in the presence of a catalyst consisting of vanadium oxide or mixtures of vanad um oxide and various promoters, and a refractory carrier such as silica, alumina, mixtures of silica and alumina, silicium carbide and the like. However, the desired acid anhydride generally is obtained in admixture with relatively large amounts of oxidation by-products. The known catalysts, in general, do not have satisfactory selectivity. For example, by oxidizing durene r l,2,4,S-tetramethylbenzene, the pyromellitic dianhydride or l,2,4,S-benzenetetracarboxylic acid dianhyide obtained contains by-products such as trimellitic acid anhydridc, 4, S-dimethylphthalic acid, and 4- methylphthalic acid anhydride. These by-products are formed at the expenses of pyromellitic dianhydride y eld and additionally. such by-products make more difficult the purification of the desired dianhydride.

Various proposals have been made for the improvement of the selectivity of the oxidation of the alkyl aromatics to the anhydride. However, modifications of the operating conditions and/or the addition of additives to the catalyst generally have led either to a decrease in the oxidation rate of the feed or to formation of combustion products. The yield of anhydride based on the amount of charged feed has not been satisfactorily increased.

An object of the present invention is to provide an improved process for the vapor-phase oxidation of hydrocarbons.

Another object of the present invention is to provide a new and improved catalyst for the vapor-phase oxidation of aromatic hydrocarbons to the corresponding 2 acid anhydride with minimum formation of by-products.

According to the present invention, a vapor-phase oxidation is presented which comprises carrying out the oxidation of alkyl aromatics having the general formula wherein R and R are alkyl radicals which may be straightor branched-chain and which contain from 1 to 6 carbon atoms and which may be the same or different, R and R are hydrogen or an alkyl radical of from I to 4 carbon atoms and which may be the same or different, the total number of carbon atoms of said alkylaromatic hydrocarbons being no greater than 18 in the presence of a catalyst consisting essentially of a carrier and vanadium oxide which is deposited on the carrier by means of hydrolysis of vanadium oxytrihalide followed by calcination of the catalyst. The halide of the vanadium oxytrihalide is one selected from the group consisting of chlorine and bromine, the oxidation temperature being between 300 and 550C.

The catalyst of the present invention is prepared by impregnating a refractory carrier with a liquid oxytrihalide of vanadium, removing the excess of oxytrihalide, hydrolyzing the oxytrihalide impregnated onto the carrier and calcining the catalyst, the halide being selected from the group consisting of chlorine and bromine. The refractory carrier, which is used in any usual form, for instance beads, pellets, cylinders, vermicelli and the like, consists of silica, alumina, mixtures of silica and alumina, silicium carbide or any other such refractory material. The liquid oxytrihalide of vanadium with which the carrier is impregnated is one prepared by reacting chlorine or bromine with vanadium oxides. Vanadium oxytrichloride is preferably used and also may be prepared by reacting thionyl chloride with vanadium pentoxide, according to the reaction V 0 3 SOCl 2 VOCl +,3 S0 During the impregnation of the carrier with vanadium oxytrihalide, it is preferred to avoid the presence of moisture and, consequently, the carrier should be previously dried. According to a preferred embodiment of the present invention, the carrier is immersed into the liquid oxytrihalide of vanadium removed and the excess of oxytrihalide thereafter removed. The immersion time depends on a number of considerations, including the nature of the carrier, the size and porosity of the carrier particles. Any other process, however, such as spraying, vapor-phase impregnation or the like, may be used, at atmospheric, superor sub-atmospheric pressure.

Water, steam or a carrier gas, such as air, which is saturated by water, is used for hydrolyzing the oxytrihalide of vanadium. This hydrolysis is carried out at a temperature which may be between 0 and l50C, preferably between about 5 and l00C and more particularly between l0 and 50C. The hydrolysis time depends on many factors, such as temperature and flow rate of the hydrolysing gas, particle size of the carrier,

3 and depth of the catalyst bed. The hydrolysis is conveniently carried out by using any method allowing an intimate contact between the carrier particles and the hydrolysing agent.

The amount of vanadium oxide on the catalyst employed in the process of the present invention may be varied within wide limits and depends principally on the particle size and porosity of the carrier. Catalysts with a high content of vanadium oxide may be prepared by carrying out successively, several impregnation and hydrolysis operations, with calcination after each hydrolysis or only after the last hydrolysis. It is preferred that the catalysts contain from 0.1 to 25% by weight, more particularly 1 to by weight, of vanadium oxide based on the weight of the final catalyst.

The catalysts of this invention may contain, in addition to vanadium oxide, other metallic oxides, such as the oxides of titanium, tin, niobium, germanium, chromium, phosphorus and the like, which act as promoters. These other metallic oxides may be incorporated into the catalyst of the present invention by treating the catalyst carrier with liquid oxytrihalide of vanadium containing a dissolved halide or any soluble salt of the metal, the oxide of which acts as a promoter. According to a preferred embodiment of the present invention, the carrier is impregnated with vanadium oxytrichloride containing dissolved therein the chloride of titanium, tin, niobium, germanium, chromium, phosphorus or a mixture of these chlorides. After the hydrolysis and calcination steps, there is obtained a catalyst impregnated with vanadium oxide together with one or more of these promotors. These promotors also may be incorporated into the catalyst before or after formation of the vanadium oxide. For instance, the catalyst carrier may be impregnated with a halide or a salt of one of the above mentioned metals or by a mixture of such halides and/or salts which are then converted into the corresponding oxides. The carrier containing the promotor(s) is then treated with the vanadium oxytrichloride or vanadium oxytribromide and the product hydrolyzed and calcinated. Additionally, the metallic promotors may be incorporated into the catalyst by using other known methods.

The amount of the promoter, if any, in the catalyst will depend upon the physical properties of the carrier, on the amount of metal halide or metal salt which is used and on the number of treatments. Catalysts containing up to 25% by weight of promotors may be prepared. However, in general, the promotor content of the catalyst usually will not exceed l0% by weight, these percentages being based on the weight of the final catalyst.

[t has been unexpectedly found that the yield of desired anhydride is improved when the oxidation is carried out in the presence of the catalysts of the present invention. Not only the amount of anhydride, but also the purity of this anhydride, are higher than those obtained using conventional catalysts under similar operating conditions.

The present process is useful for the oxidation of such aromatic hydrocarbons as naphthalene, octahydroanthracene and polyalkylbenzenes having at least two alkyl substituents, which may be the same or different, in ortho position. These polyalkylbenzenes include l,2-dimethylbenzene or ortho-xylene, l-methyl-Z- butyl-benzene, l,2-diisopropylbenzene, 1,2-diethylbenzene, l-methyl-2(4-methylpentyl)benzene, l-methyl-2-isopropylbenzene, l -methyl-2-propylbenzene,

l ,2,4,5-tetraethylbenzene, l ,2,4,S-tetraisopropylbenzene, l,2,4,5-tetramethy1benzene or durene, and the like. Anhydrides of the corresponding benzenepolycarboxylic acids, namely o-phthalic anhydride and pyromellitic dianhydride, are obtained by oxidizing the above cited hydrocarbons.

The present vaporphase oxidation process is carried out at temperatures generally, of from 300 to 550C, although temperatures outside these limits may be employed in some circumstances. The temperature depends principally on the feed. For instance, o-xylene is preferably oxidized at a temperature of from 325 to 475C while durene is preferably oxidized at 350-450C. Pressure may also be varied, but the oxidation is generally performed at about atmospheric pressure. The other operating conditions, such as the relative proportions and rates of flow of the reactants, and other features of the process, are substantially the same as in the processes generally used for oxidizing aromatic hydrocarbons into anhydrides of benzenepolycarboxylic acids.

In order to more fully describe and to exemplify the present invention, the following examples are presented. These examples are not to be construed as in any manner limiting the present invention.

EXAMPLE 1 A catalyst carrier (400 ml) consisting essentially of silicium carbide and containing 25 to 30% of SiO and in the form of beads with an average diameter of 4.7 mm, was calcinated during 1 hour at 350C. There was obtained 372.5 g of catalyst carrier. This carrier was introduced into a Pyrex cylindrical reactor (diameter: 79 mm; height: 200 mm) having 3 apertures at the top and 1 aperture at the bottom. One of the top apertures was used to introduce vanadium oxytrichloride. The other top apertures were respectively used for the removal of the exhaust gases and for the removal of the vapors which were formed during the hydrolysis. The bottom aperture was used to remove the excess of VOCl and to introduce the hydrolysis agent. The lower part of the reactor contained a bed (depth: 20 mm) of aluminium Raschig-rings. A current of dry and pure nitrogen to remove the moisture was passed over the catalyst carrier in the reactor for 30 minutes.

VOCl was introduced in an amount (225 ml) such that the carrier was completely immersed by this liquid, at 25C. After 15 minutes, the excess of VOCl was withdrawn, a current of nitrogen being introduced through the top of the reactor to aid in draining the liquid. The VOCl was then hydrolyzed during 1 hour by passing into contact therewith at 25C a stream of air saturated with water, this air being introduced through the bottom of the reactor at a rate of 1200 liters/hour. The catalyst was then removed from the reactor, dried by passing dry air thereover for 16 hours at C and then calcinated during 1 hour at 500C. This catalyst contained 4.9% by weight of vanadium oxide.

A mixture of durene and air containing 0.2 vol. durene was introduced into a Pyrex reactor containing a fixed bed of 60 ml. of the above prepared catalyst. The catalyst, in the form of beads, was in admixture with Pyrex beads having the same size as the catalyst beads. The oxidation was carried out at 390C and atmospheric pressure, and by using 40 g. of durene per liter of catalyst per hour. This run was referred to as Run 1. For comparison, two other similar runs, referred to as Run 2 and Run 3, were carried out under the same conditions but with other catalysts. Run 2 employed a catalyst containing 5.3 weight of vanadium oxide prepared by known methods from ammonium meta-vanadate. Run 3 employed a catalyst containing 6.8 weight of vanadium oxide prepared by known methods from vanadium oxalate. For each run, the weight yield of crude pyromellitic dianhydride (or solid products ob tained by the oxidation and containing this dianhydride in admixture with other oxidation products) and the purity of the dianhydride (or amounts of dianhydride in this mixture) were determined and were used to calculate the yield of pure dianhydride of pyromellitic acid or PMDA based on the feed.

The process described in Example I was substantially repeated by oxidizing durene in the presence of a catalyst in the form of beads of silicium carbide containing 4.9% by weight of vanadium oxide and 0.3% by weight of titanium oxide. This catalyst was prepared as above described from vanadium oxytrichloride containing dissolved therein titanium tetrachloride. The yield of PMDA as a function of the temperature was the follow- Temperature Yield of PMDA (weight 366C 72.5% 380C 97.3% 395C 85.9%

For comparison, a run was carried out in the presence of a catalyst containing 4.9% by weight vanadium oxide (prepared from ammonium meta-vanadate) and 0.5%

as that employed in Run 1 of Example 1 except that the finished catalyst contained 7.1% by weight vanadium oxide. The conditions of this oxidation were those employed in Example 1 except for temperature which was varied as below set forth. The yield of phthalic anhydride as a function of the oxidation temperature was as follows:

Temperature Yield (wt. '36) For comparison, similar runs were carried out at temperatures of from 360 to 490C, in the presence of a catalyst containing 7.1% by weight vanadium oxide prepared from ammonium oxalate. The best yield of phthalic anhydride was 71.9%.

EXAMPLE 5 Example 2 was substantially repeated except that l',2,4-trimethyl-5-isopropylbenzene was the feed. PMDA was obtained with a selectivity higher than 80%.

EXAMPLE 6 A catalyst prepared as described in Example I and containing 7.1% by weight of vanadium oxide was used for the vapor-phase oxidation of naphthalene at 415C. Phthalic anhydride was obtained with a yield of 76 wt.

EXAMPLES 7 to 9 Example Feed Oxidation Anhydride temperature ("C) 7 octahydroanthracene 420 Pyromellitic 8 l,methyl-2-butyl-benzene 410 Phthalic 9 l,2,4,5-tetraisopropylbenzene 390 Pyromellitic b wei ht titanium oxide. The best ield of PMDA was y 8 y EXAMPLE 10 EXAMPLE 3 ing 4.7% by weight of vanadium oxide and 0.5% of chromium oxide, prepared from vanadium oxytrichloride containing dissolved chromium oxide. The oxidation was carried out at 375C. The yield of pure PMDA was 58.2 wt.

EXAMPLE 4 The vapor-phase oxidation of o-xylene was carried out in the presence of a catalyst substantially the same A catalyst as described in Example I was prepared. However, the catalyst carrier was first impregnated with titanium chloride, hydrolyzed and calcined and thereafter impregnated by vanadium oxytrichloride, hydrolyzed and calcined. The catalyst contained 5.25 wt. of vanadium oxide and 0.94 wt. of titanium oxide. Durene was oxidized with this catalyst as described in Example l, but at a temperature of 380C. PMDA was obtained with a yield of 82.4% by weight.

What is claimed is:

l. A process for producing anhydrides of benzenepolycarboxylic acids by the vapor-phase oxidation of aromatic hydrocarbons selected from the group consisting of naphthalene, octahydroanthracene and polyalkylbenzenes containing at least two alkyl substitue nts in ortho position to one another and having the general formula wherein R and R are alkyl radicals having a straight or branched chain and containing 1 to 6 carbon atoms and R and R are radicals selected from the group consisting of hydrogen and alkyl radicals containing 1 to 4 carbon atoms, the total number of carbon atoms of said polyalkylbenzenes being no higher than 18, said process comprising oxidizing said aromatic hydrocarbons at a temperature of between about 300 and 550C and in the presence of a catalyst consisting of a refractory carrier and vanadium oxide, said catalyst prepared by impregnating said refractory carrier with an oxytrihalide of vanadium in which the halide is selected from the group consisting of chlorine and bromine, hydrolyzing said oxytrihalide of vanadium and then calcining said catalyst.

2. The process of claim 1 wherein said aromatic hydrocarbon is one selected from the group consisting of naphthalene and o-xylene and wherein said temperature is between about 325 and 500C.

3. The process of claim 1 wherein said aromatic hydrocarbon is selected from the group consisting of octahydroanthracene and tetramethylbenzene, and

wherein said temperature is between about 300 and 500C.

4. The process of claim 1 wherein said oxytrihalide of vanadium is vanadium oxytrichloride.

5. The process of claim I wherein a metal oxide promotor is employed in admixture with said vanadium oxide in said catalyst.

6. The process of claim 5 wherein said metal oxide promotor is an oxide of a metal selected from the group consisting of titanium, tin, niobium, germanium, chromium, phosphorus, and mixtures thereof.

7. The process of claim 5 wherein said metal oxide promotor is placed on the refractory carrier prior to impregnation thereof with the vanadium oxytrihalide.

8. The process of claim 5 wherein said metal oxide promotor is placed on the refractory carrier by dissolving a soluble salt of the metal in said oxytrihalide of vanadium and impregnating said refractory carrier with the solution and thereafter hydrolyzing the salts to the oxide.

9. The process of claim 1 wherein said catalyst contains 0.1 to 25% by weight of vanadium oxide.

10. The process of claim 1 wherein said catalyst contains l to 10% by weight of vanadium oxide.

11. The process of claim 5 wherein said metal oxide promotor is present in an amount of 0.! to 25% by weight of said catalyst.

12. The process of claim 1, wherein said catalyst is prepared by the steps consisting essentially of impregnating said refractory carrier with an oxytrihalide of vanadium in which the halide is selected from the group consisting of chlorine and bromine, hydrolyzing said oxytrihalide of vanadium and then calcining said catalyst.

i -twinn- 

1. A PROCESS FOR PRODUCING ANHYDRIDES OF BENZENEPOLYCARBOXLIC ACIDS BY THE VAPOR-PHASE OXIDATION OF AROMATIC HYDROCARBONS SELECTED FROM THE GROUP CONSISTING OF NAPHTHALENE, OCTAHYDROANTHRACENE AND POLYALKYLBENZENES CONTAINING A LEAST TWO ALKYL SUBSTITUENTS IN ORTHO POSITION TO ONE ANOTHER AND HAVING THE GENERAL FORMULA
 2. The process of claim 1 wherein said aromatic hydrocarbon is one selected from the group consisting of naphthalene and o-xylene and wherein said temperature is between about 325* and 500*C.
 3. The process of claim 1 wherein said aromatic hydrocarbon is selected from the group consisting of octahydroanthracene and tetramethylbenzene, and wherein said temperature is between about 300* and 500*C.
 4. The process of claim 1 wherein said oxytrihalide of vanadium is vanadium oxytrichloride.
 5. The process of claim 1 wherein a metal oxide promotor is employed in admixture with said vanadium oxide in said catalyst.
 6. The process of claim 5 wherein said metal oxide promotor is an oxide of a metal selected from the group consisting of titanium, tin, niobium, germanium, chromium, phosphorus, and mixtures thereof.
 7. The process of claim 5 wherein said metal oxide promotor is placed on the refractory carrier prior to impregnation thereof with the vanadium oxytrihalide.
 8. The process of claim 5 wherein said metal oxide promotor is placed on the refractory carrier by dissolving a soluble salt of the metal in said oxytrihalide of vanadium and impregnating said refractory carrier with the solution and thereafter hydrolyzing the salts to the oxide.
 9. The process of claim 1 wherein said catalyst contains 0.1 to 25% by weight of vanadium oxide.
 10. The process of claim 1 wherein said catalyst contains 1 to 10% by weight of vanadium oxide.
 11. The process of claim 5 wherein said metal oxide promotor is present in an amount of 0.1 to 25% by weight of said catalyst.
 12. The process of claim 1, wherein said catalyst is prepared by the steps consisting essentially of impregnating said refractory carrier with an oxytrihalide of vanadium in which the halide is selected from the group consisting of chlorine and bromine, hydrolyzing said oxytrihalide of vanadium and then calcining said catalyst. 